Scientists have made a major

【题目】Scientists have made a major ________ in the treatment of cancer.

A. barrier    B. breakthrough

C. companion    D. concern

【答案】B

【解析】

考查名词词义辨析。句意：科学家在癌症治疗方面取得了重大突破。A. barrier障碍物；B. breakthrough突破；C. companion 同伴；D. concern关心。短语make a breakthrough突破。故选B。